Borax-Perlentest auf Metallionen

Identifikation von Übergangsmetallen anhand farbiger Glasperlen aus der Boraxschmelze

Qualitative Analysis Intermediate (High School) 45 Min. ~$8,00

Ziel

Übergangsmetallionen anhand der charakteristischen Farben identifizieren, die sie beim Einschmelzen in eine Borax-(Natriumtetraborat-)Glasperle erzeugen.

Hintergrund

The borax bead test is an elegant method for identifying transition metal ions. When borax (Na₂B₄O₇·10H₂O) is heated, it loses water and forms a clear glassy bead of sodium metaborate. When a metal salt is dissolved into this bead, the metal ions become trapped in the glass matrix, producing characteristic colors. The color often differs between the oxidizing flame (outer cone) and reducing flame (inner cone), providing additional diagnostic information.

Sicherheitswarnungen

  • Molten borax beads are extremely hot
  • Chromium compounds are irritants — avoid dust inhalation
  • Do not touch hot beads — let cool on a watch glass
  • Cobalt compounds are toxic if ingested

Erforderliche PSA

goggles gloves lab_coat

Materialien

  • Borax (Na₂B₄O₇·10H₂O) (5 g)
    Powdered
  • Metal salt samples (0.5 g each)
    CuSO₄, CoCl₂, NiCl₂, FeCl₃, MnCl₂, Cr₂O₃
  • Unknown metal salt (0.5 g)

Ausrüstung

Platinum wire loop (or nichrome alternative) Bunsen burner Forceps Watch glasses (7)

Durchführung

1

Make a small loop at the end of the platinum wire. Heat the loop in the hottest part of the flame until red-hot.

2 Min. Wire is very hot
2

Dip the hot wire into powdered borax. Return to the flame and heat until a clear, transparent glass bead forms. Repeat dipping and heating if needed to build up the bead.

5 Min.
3

Touch the hot bead to a tiny amount of CuSO₄ powder. Return to the oxidizing flame (outer cone). Observe the color (should be blue-green).

5 Min.
4

Now heat the same bead in the reducing flame (inner cone, blue). The color may change to red (metallic copper).

3 Min.
5

Make fresh beads and repeat for each metal salt. Record colors in both oxidizing and reducing flames, both hot and cold.

20 Min.
6

Test the unknown salt and match the bead colors to your reference chart.

10 Min.

Erwartete Ergebnisse

Cu: blue-green (oxidizing), red (reducing). Co: deep blue (both). Ni: gray-brown (oxidizing), gray (reducing). Fe: yellow-brown (oxidizing), green (reducing). Mn: violet (oxidizing), colorless (reducing). Cr: green (both, darker in reducing).

Aufräumen

Allow all beads to cool completely. Dispose of transition metal waste appropriately. Clean the platinum wire by fusing with fresh borax until clear.

Details

Kategorie
Qualitative Analysis
Schwierigkeit
Intermediate (High School)
Dauer
45 Min.
Geschätzte Kosten
$8,00
Schritte
6
Materialien
3

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Frequently Asked Questions

What is the objective of Borax-Perlentest auf Metallionen?
Übergangsmetallionen anhand der charakteristischen Farben identifizieren, die sie beim Einschmelzen in eine Borax-(Natriumtetraborat-)Glasperle erzeugen.
How difficult is Borax-Perlentest auf Metallionen?
This experiment is rated as Intermediate (High School). It takes approximately 45 minutes to complete.
What safety precautions are needed for Borax-Perlentest auf Metallionen?
Key safety precautions include: Molten borax beads are extremely hot; Chromium compounds are irritants — avoid dust inhalation; Do not touch hot beads — let cool on a watch glass.
What materials are needed for Borax-Perlentest auf Metallionen?
The main materials required are: Borax (Na₂B₄O₇·10H₂O), Metal salt samples, Unknown metal salt.
What results should I expect from Borax-Perlentest auf Metallionen?
Cu: blue-green (oxidizing), red (reducing). Co: deep blue (both). Ni: gray-brown (oxidizing), gray (reducing). Fe: yellow-brown (oxidizing), green (reducing). Mn: violet (oxidizing), colorless (reducing). Cr: green (both, darker in reducing).